The bar line devides the staff into measures.
yesunless it has two dots next to it (repeat sign) or there are two of them (end of the song)
maybe i can be of help- i don't know there exact name, but their purpose is to divide the music into measures
measures
Two lines are perpendicular when the cross product of their director vectors is equal to one. Example A = (1,0,0) B= (0,1,0) A x B = 1 then A is perpendicular to B